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Bi2Te3基温差电材料薄膜和一维纳米线的电化学制备、表征及形成机理研究
Investigations on the Electrochemical Preparation, Characterization and Forming Mechanism of Bi2Te3 Based Thermoelectric Thin Films and Nanowires
【作者】 黄庆华;
【导师】 王为;
【作者基本信息】 天津大学 , 应用化学, 2005, 博士
【摘要】 低维温差电材料在温差制冷和温差发电方面展现的广阔应用前景引起了科学界的普遍关注。本论文以电化学技术制备Bi2Te3基温差电材料为目的,通过循环伏安、交流阻抗、阴极极化等电化学测试技术对含有Bi3+、HTeO2+和SbO+的单组分溶液体系、二元溶液体系及三元溶液体系的电化学性能进行了系统研究,提出了具体的反应机理。在理论研究基础上,结合ESEM、FETEM、HREM、SEAD、XPS、XRD、EDS、EDX等现代物理测试技术对电沉积Bi2Te3和Bi2-xSbxTe3温差电薄膜及纳米线阵列的形貌、结构、组成及性能等进行了表征,并对影响温差电性能的因素进行了深入的探讨。由于离子间相互作用的结果,Bi3+、HTeO2+和SbO+在Bi-Te体系、Sb-Te体系和Bi-Sb-Te三元体系中的电化学行为完全不同于各个单组分体系。研究表明HTeO2+在混合溶液的整个电沉积过程中具有非常重要的作用,它能够吸附在铂电极表面而首先被还原,再与其它离子反应生成相应的化合物。采用电化学恒电位沉积技术制备了Bi2Te3及Bi2-xSbxTe3薄膜温差电材料,通过控制沉积电位可以调节薄膜的组成,影响材料的温差电性能,进而能够根据需要设计材料,进行有目的的电化学合成。电沉积Bi2Te3薄膜为n型半导体,-0.030V是最佳沉积电位,其塞贝克系数约为-44μV?K-1。而Bi2-xSbxTe3薄膜为p型半导体,控制沉积电位为-0.5V条件下电沉积薄膜的塞贝克系数达最大,为213μV·K-1,其组成为Bi0.5Sb1.5Te3。在室温范围内,电沉积Bi2-xTe3+x和Bi2-xSbxTe3温差电薄膜的塞贝克系数均随温度的升高呈现上升的趋势,而薄膜电阻却不断降低。此外,多元掺杂能够提高材料的电导率,是改善材料温差电性能的有效方法。以多孔氧化铝薄膜为模板,通过直流电沉积技术成功制备了Bi2Te3和Bi2-xSbxTe3一维纳米线温差电材料。恒电位沉积的Bi2Te3纳米线为多晶体,具有六方晶体结构。恒电流沉积的Bi2-xSbxTe3纳米线的组成随着沉积电流的变化而改变,因此可以通过调节沉积电流的大小控制纳米线的组成,进而改善材料的温差电性能。纳米线阵列的塞贝克系数远远小于块状材料,成分分布不均匀以及纳米线直径较大是影响性能提高的主要原因。
【Abstract】 Low dimensional thermoelectric materials have attacted much attention due to their extensive application on pelter coolers and power generators. The purposes of this dissertation are to electrochemically fabricate Bi2Te3 based nanostructured thermoelectric materials. The reduction process for unitary, binary and ternary system of Bi3+, HTeO2+, SbO+ in acid nitric medium was investigated by means of cathodic polarization, cyclic voltammetry and electrochemical impedance measurements. The mechanisms were developed to direct the production of Bi2Te3 and Bi2-xSbxTe3 thermoelectric films and nanowire arrays. By using ESEM, FETEM, HREM, SEAD, XPS, XRD, EDS and EDX techniques, the morphology, structure, composition, and properties of the deposited materials were examined. And the factors influencing thermoelectric performances of the thin films and nanowire arrays were thoroughly studied.The electrochemical behaviors of Bi3+, HTeO2+ and SbO+ in Bi-Te, Sb-Te and Bi-Sb-Te system are different from that of monocomponent system because of ion interaction. HTeO2+ plays important role in the whole reduction process, which can be reduced firstly because of its strong adsorption on the surface of the Pt electrode, then react with other ions to form the proper compounds.The Bi2Te3 and Bi2-xSbxTe3 thermoelectric thin films were prepared by potentiostatic electrodeposition. The composition of the film and its thermoelectric properties can be controlled through adjusting electrodeposition potential, so the synthesis of the materials can be easily performed according to the actual requirements. N-type semiconductive film of Bi2Te3 was prepared at the potential of -0.030V with the largest seebeck coefficient of -44μV·K-1. The Bi2-xSbxTe3 film is p-type semiconductor and when to be electrodeposited at -0.5V it possesses the largest seebeck coefficient of 213μV·K-1, whose composition was proved to be Bi0.5Sb1.5Te3. When the temperature increased in the scope of 300~350K, the seebeck coefficient of the Bi2Te3 and Bi2-xSbxTe3 thermoelectric thin films increased while their resistance reduced, which means that they can be used under room temperature. In addition multidoping is the effective method for improving the thermoelectric properties of materials.The Bi2Te3 and Bi2-xSbxTe3 thermoelectric nanowire arrays have beensuccessfully fabricated by direct current deposition respectively in porous anodic aluminum oxide template. The potentiostatic deposits of Bi2Te3 nanowires are polycrystalline with hexagonal structure. The compostion of the galvanostatic deposits of Bi2-xSbxTe3 nanowires is determined by the current, so the thermoelectric properties of the nanowires can be controlled through adjusting electrodeposition current. The seebeck coefficient of nanowire arrays is much lower than that of bulk materials. The main factors to affect the thermoelectric performance are uneven distribution of the composition and the large diameter of the nanowires.
【Key words】 Bi2Te3; Bi2-xSbxTe3; thermoelectric material; thin film; nanowire array; electrodeposition; seebeck coefficient;